Pressure sensitive recording paper

ABSTRACT

WHEREIN N IS AN INTEGER OF 1 TO 8, R and R&#39;&#39; each represent a member selected from the group consisting of alkyl groups containing one to eight carbon atoms, and a hydrogen atom, p and q represent the number of alkyl groups, p + q being an integer of 1 to 3, and R and R&#39;&#39; may be the same.   A pressure-sensitive recording paper comprising a support having coated thereon a layer of color former, said color former dissolved in at least one compound represented by the following formula:

United States Patent Kiritani et al.

[ Sept. 17, 1974 PRESSURE SENSITIVE RECORDING PAPER [75] inventors:Masataka Kiritani; Hiroharu Matsukawa, both of Shizuoka; Masayuki Aoki,Kanagawa, all of Japan [73] Assignee: Fuji Photo Film Co., Ltd.,

Kanagawa, Japan [22] Filed: Oct. 27, 1971 [21] Appl. No.: 193,151

[30] Foreign Application Priority Data Oct. 27, 1970 Japan 45-94877 [52]US. Cl 117/36.2, 8/94, 117/368, 252/316 [51] Int. Cl. B4lc 1/06 1. .8..7 i ldetSvsersletg: 117/36-2 -8 13. 6 8/94 [56] References Cited UNITEDSTATES PATENTS 3,009,760 11/1961 Lenz 8/94 3,016,308 l/l962 MacAulay1l7/36.l 3,625,736 12/1971 Matsukawa ll7/36.2 3,627,581 12/l97l Phillips117/362 3,649,649 3/1972 Orita et al ll7/36.2

FOREIGN PATENTS OR APPLICATIONS 915,342 l/1963 Great Britain 8/94Primary Examiner-William D. Martin Assistant Examiner-Bernard D.Pianalto Attorney, Agent, or FirmSughrue, Rothwell, Mion, Zinn & Macpeak[5 7] ABSTRACT A pressure-sensitive recording paper comprising a supporthaving coated thereon a layer of color former, said color formerdissolved in at least one compound represented by the following formula:

7 Claims, No Drawings PRESSURE SENSITIVE RECORDING PAPER BACKGROUND OFTHE INVENTION 1. Field of the Invention This invention relates to apressure-sensitive recording paper. More particularly, it relates to apressuresensitive recording paper using a compound, in which twoalkyl-substituted benzene nuclei are connected with each other throughthe unit 4C,,H as a solvent for a color former:

wherein n is an integer of from 1 to 8, R and R each is an alkyl grouphaving one to eight carbon atoms or a hydrogen atom, p and q each is thenumber of alkyl groups, p q being an integer of 1-3, and wherein R and Rmay be the same.

2. Description of the Prior Art The object of the present invention isto obtain a pressure-sensitive recording paper having no unpleasantsmell and toxicity, and capable of forming a color image having a higherdensity without giving a color fog.

Usually, as pressure-sensitive recording paper, there are thosecomprising so-called upper paper prepared by dissolving a substantiallycolorless compound (hereinafter referred to as a color former) in anorganic solvent, encapsulating it, and then coating the capsules onto asupport; lower paper prepared by coating a color-developing material(hereinafter referred to as a color developer), which is capable offorming colored images, onto another support; and, in some cases, middlepaper prepared by coating capsules containing a color former onto oneside of a support and a color developer onto the other side thereof, orthose containing said capsules and a color developer onto the same sideof a support.

ln the case of the combination of upper and lower paper, or upper,middle and lower paper, color is developed by locally pressing in such away that the capsule layer comes into contact with the color developerlayer to decompose the capsules located at the pressed part and to causereaction between the color former and the color developer. When apressure sensitive recording paper having capsules and a color developeragent on the same surface thereof is used. color will be developed bypressing in the same way. As the color developer, active clay materials,such as acid clay, active zeolite and bentonite, or organic acidicmaterials, such as succinic acid, tannic acid, gallic acid,pentachlorphenol and phenol resin are generally used. As a color formerfor a pressure sensitive recording paper, malachite green lactone,benzoyl leucomethylene blue, crystal violet lactone, rhodamine B lactom,3-dialkylamino-7- alkylfluorans, 3-methyl-2,2-spirobi(benzo[f]chromene), etc. are used.

The conditions a solvent dissolving a color former for pressuresensitive recording paper should satisfy are:

a. to have enough solubility to dissolve a necessary amount of colorformer,

b. to have a high boiling point so as not to vaporize in a heat-dryingprocess and in a place of elevated temperature,

c. not to be eluted on encapsulation,

d. not to desensitize or prevent the color formation on the lower paper,

e. not to provide changes, such as decomposition of the color former,color formation, etc.,

f. to have a low viscosity so that the effusion thereof from inside thecapsules can be freely done on breakage of the capsules, and to have asmall rise in viscosity, even at a low temperature,

g. to have no unpleasant smell,

h. to have little toxicity to human beings and animals,

and the like. Among these, conditions (a)-(e) are especially ofimportance and, if one of these conditions is not satisfied, the solventcannot be used as a solvent for a color former.

In fact, however, solvents satisfying conditions of said (a)-(h) have sofar not been found. Therefore, as things are, those prepared by mixingseveral kinds of solvents in a suitable ratio are used.

That is, ethers do not satisfy the conditions of (a) and (d), alcoholsdo not satisfy the conditions of (a), (c) and (d), paraffins do notsatisfy the conditions of (a), ketones, esters, olefins and amines donot satisfy the conditions of (d), and organic acids do not satisfy theconditions of (c), and usual aromatic hydrocarbons do not satisfy theconditions of (a), (g) and (h). Chlorinated diphenyl now used as asolvent for pressure sensitive recording paper, nearly satisfies theconditions of (a) to (e). It has, however, defects in that, at a lowchlorination degree, it has a peculiar unpleasant smell, while it haslow viscosity and that, at high chlorination degree, it has highviscosity, and does not have much of an unpleasant smell. That is, theviscosities of low chlorinated trichlorodiphenyl and tetrachlorodiphenylare comparatively low. However, they have a peculiar unpleasant smell.Highly chlorinated pentachlorodiphenyl and hexachlorodiphenyl haveconsiderably reduced unpleasant smell, but their viscosity conspicuouslyincreases on the other hand. Hexachlorodiphenyl has no fluidity at aroom temperature. Therefore, the pressure-sensitive recording paperwherein low chlorinated trichlorodiphenyl and tetrachlorodiphenyl areused, has the defect of having an unpleasant smell. The pressuresensitive recording paper wherein highly chlorinated pentachlorodiphenyland hexachlorodiphenyl are used, has the defect in that the effusionthereof is difficult to be freely done due to their high viscosity andthat sufficient color density cannot be obtained, while they have lessof an unpleasant smell. The pressure-sensitive recording paper whereinthe mixture of chlorinated diphenyl with a low chlorination degree andthe same with high chlorination degree is used, is a little moreimproved in the smell than that wherein chlorinated diphenyl with lowchlorination degree is used separately and, in the density of the colorformed, the former is a little more improved than that wherein highlychlorinated diphenyl is used independently, but the former has stillconsiderable unpleasant smell and the density of color formed is notsufficient. in addition, chlorinated diphenyl is slightly decomposed bylight to form hydrogen chloride. Accordingly, the capsule coated sheetwherein chlorinated diphenyl is used has the defect that, when it isexposed to light for a long time, the generated hydrogen chloride willbe reacted with the color former to cause colored fog. Furthermore, thiscapsule coated sheet wherein the colored fog took place has less colordeveloping ability onto the lower paper, and a sufficient density of thecolor formed cannot be obtained. Besides, chlorinated diphenyl hasappreciable toxicity to human beings and animals. Therefore, theconventional pressure sensitive recording paper wherein chlorinateddiphenyl is used, has had the defects that it has unpleasant smell, thatsufficient density of the color formed cannot be obtained, that whenexposed to light for a long time, colored fog on capsule coated sheetand the lowering of the color developing ability thereof to the lowerpaper take place, and that it has a problem in its toxicity.

SUMMARY OF THE INVENTION We, the inventors, as the result of manyinvestigations concerning these kind of solvents, have found that thespecific compound represented by the general formula I has propertieswhich are quite adequate for our purpose, and accomplished thisinvention. That is, the present invention is characterized in that, inthe pressure sensitive recording paper, the compound represented by thegeneral formula (I) is used as a solvent for the color former,separately or in combination with other solvents.

The compound (I) in this invention is characterized in that two alkylsubstituted benzene nuclei are connected with each other through a-(-C,,H bond and, as is different from the usual aromatic compounds, thecompound (I) of the present invention has a considerably high boilingpoint, does not vaporize off in a heat drying process or in a place ofthe elevated temperature, has no unpleasant smell, and in addition, ithas no toxicity to human beings and animals.

DETAILED DESCRIPTION OF THE INVENTION The reason why p q in the compound(I) used in the present invention is restricted to not more than 3, isthat, when p q is not less than 4, the viscosity thereof conspicuouslyincreases or the compound becomes solid, which is not desirable.

The reason why the number of the carbon atoms contained in R and R, andthat in the (-C,,H existing between the two benzene nuclei is not morethan 8 and 8, respectively, is that, when the number of the carbon atomscontained in R and R becomes not less than 9 and n becomes not less than9, the viscosity thereof conspicuously increases and the solubility of acolor former thereto decreases, which is not desirable.

The compound of this invention having a particularly restrictedstructure, satisfies the aforesaid conditions of (a)(e) demanded for asolvent for the color former of pressure sensitive recording paper. Inaddition, it has the excellent advantages that there is little rise inviscosity, even at a low temperature, that it has no unpleasant smell ortoxicity to human beings and animals, that it raises the stability ofthe capsule coated sheet to light, that, even when the capsule coatedsheet is exposed to light for a long time, the colored fog of the sheetis remarkably less compared with conventional ones, that the colordeveloping ability in developing this capsule coated sheet onto thelower paper does not decrease like the conventional ones, and the like.The pressure sensitive recording paper of this invention is excellentalso in that it has a higher density with respect to the color formedcompared with conventional pressure sensitive recording paper, whereinchlorinated diphenyl is used. Therefore, it can be said that thecompound (I) used in the present invention having a particularlyrestricted structure is extremely excellent as a solvent for a colorformer of pressure sensitive recording paper.

The compound of the general formula (I) of the present invention may beused in combination with other solvents. As solvents to be mixedtogether, there are petroleum fractions such as liquid paraffin,kerosene, naphtha, etc., synthesized oils, such as chlorinated paraffin,chlorinated diphenyl, hexahydroterphenyl, alkylnaphthalenes, alkylatedpolyphenyls, etc., and vegetable oils, such as cotton seed oil, linseedoil, etc. These solvents are mixed and used together in order to adjustthe viscosity, to control the solubility of a color former, and toincrease the quantity for the reduction of cost, etc.

This invention is characterized by using the compound of the generalformula (I) having a particularly restricted structure as a solvent fora color former of pressure sensitive recording paper and, accordingly,all of the publicly known art can be applied as a method or process forencapsulating this solvent. Therefore, the present invention is notrestricted by the method or process for the encapsulation.

The present invention will be further explained by the followingExamples, which are merely illustrative and not limitative of thepresent invention.

In the examples of the present invention, there is used a clay paper(lower paper) prepared as follows. That is, g of sulfuric acid processedacidic terra abla was dispersed in 280 g of water containing 6 g of 40percent sodium hydroxide aqueous solution using homogenizer. Thereafter,50 g ofa 10 percent aqueous solution of sodium salt of casein and 30 gof a styrene butadiene latex (trade name: Dow Latex 626, made by DowChemical Co.), were added thereto as a binder, and coated on a paper byair knife coating, and dried to obtain the clayed paper.

EXAMPLE 1 To 100 g of 2,4-dimethyldiphenylmethane obtained by thereaction between meta-xylene and benzyl chloride, having the followingformula (b.p. 295 296C/760 mmI-Ig, specific gravity (DP) 0.9951);

was dissolved 3 g of crystal violet lactone. The resulting solution wasthen added to a solution of 20 g of gum arabic and g of water toemulsify. Thereafter, 20 g of acid processed gelatin and 160 g of waterwere added thereto and the pH thereof was reduced to 5 by the additionof acetic acid under constant stirring, 500 g of water was then added tocause coacervation. 0n coacervation, a dense liquid membrane ofgelatin-gum arabic was formed around the oil droplets containing a colorformer. The pH was further reduced to 4.4, and 4 g of 37 percentformalin was successively added for hardening the membrane. Saidoperation was carried out keeping the temperature of the system at atemperature of 50C. Then the system was cooled to 10C in order to gelthe dense liquid membrane. Furthermore, in order to raise the effect ofhardening, the pH thereof was raised to 9 and the system was allowed tostand for several hours to accomplish the encapsulation. The capsulesolution thus obtained was coated on a sheet of paper by air knifecoating, then dried. The pressure sensitive recording paper thusobtained had no unpleasant smell like that of the conventional pressuresensitive recording paper wherein chlorinated diphenyl was used as asolvent. When this paper (upper paper) was superposed on a clay paper(aforesaid lower paper coated with active clay substance) and writingwas conducted with pressure, there was developed a blue image on aclayed paper in an instant. The density of this color developed imagewas remarkably high compared with that of the conventional pressuresensitive recording paper. In addition, even when this upper paper wasexposed to sun light for a long time, the lowering in the colordeveloping ability and colored fog were not recognized.

EXAMPLE 2 3 g of rhodamine B lactam was dissolved in 100 g of2,5-dimethyldiphenylmethane obtained by the reaction between para-xyleneand benzyl chloride, having the following formula (b.p. 293.5 294.5C/760mml-lg, specific gravity (D 0.9950);

and treated in the same manner as in Example 1 to obtain upper paper.The upper paper thus obtained had no unpleasant smell like that of theconventional pressure sensitive recording paper. When this upper paperwas superposed on a clay paper and writing was conducted with pressure,there was developed red image on a clay paper in a moment. The densityof color developed image was remarkably high compared with that of theconventional recording paper wherein chlorinated diphenyl was used.Besides, even when this upper paper was exposed to sun light for a longtime, the lowering in the color developing ability and fog were notobserved.

EXAMPLE 3 2 g of 3-diethylamino-7-methylfluoran was dissolved in amixture of 80 g of octadecyldiphenylmethane having the followingstructure (mixture of several kinds of isomers, b.p. 232-244Cll0 mmHg);

and 20 g of paraffin containing l0-l2 carbon atoms, treated in the samewas as in Example 1 to obtain upper paper. The upper paper for pressuresensitive recording paper thus obtained had no unpleasant smell likethat of the conventional pressure sensitive recording paper prepared bythe analogous treatment using chlorinated diphenyl. When this upperpaper was superposed on a clay paper and writing was conducted withpressure, there was developed a red image on a clay paper. The densityof this color developed image was remarkably high compared with that ofthe conventional pressure sensitive recording paper wherein chlorinateddiphenyl CaHn was used. In addition, even when this upper paper wasexposed to sun light for a long time, the lowering in the colordeveloping ability and colored fog were not observed.

EXAMPLE 4 on; on; V

and 30 g of isoparaffin containing 12 14 carbon atoms, treated in thesame way as in Example 1 to obtain upper paper. This upper paper had nounpleasant smell like that of the conventional pressure sensitiverecording paper wherein chlorinated diphenyl was used. When this upperpaper was superposed on a clay paper and writing was done with pressure,there was developed a blackish green image on a clay paper. The densityof this color developed image was remarkably high compared with that ofthe conventional pressure sensitive recording paper wherein chlorinateddiphenyl was used. In addition, even when this upper paper was exposedto sun light for a long time, the lowering in the color developingability and colored fog were not observed.

EXAMPLE 5 0.2 g of 3-diethylamino-7-diethylaminofluoran was dissolved in20 g of l,l-di-p-toluylethane (having a melting point lower than 20C anda boiling point of 295 300C/760 mml-lg) represented by the followingstructure:

-Q CH and to this were added 5 g of toluylenediisocyanate and 10 g ofmethylene chloride containing 3 g of bisphenol A to prepare a firstsolution. Thereafter, 3 g of polyvinyl alcohol was dissolved in 25 g ofwater, and to this was added said first solution under vigorous stirringto emulsify. The resulting emulsion was poured into 150 g of water keptat 50C, and the temperature of the system was raised to C understirring. The system was maintained at this temperature for 30 minutesto cause polymerization between the toluylenediisocyanate and bisphenolA on the surface of the oil droplets to form a capsule wall, wherebyencapsulation was accomplished. The capsule solution thus obtained wascoated on a paper by way of roll coating, then dried. The upper paperobtained in this way did not have the unpleasant smell like that of theconventional pressure sensitive recording paper obtained by theanalogous treatment using chlorinated diphenyl. When this upper paperwas superposed on a clay paper and writing was conducted, there wasdeveloped a blackish green image on a clay paper. The density of thiscolor developed image was remarkably high compared with that of theconventional pressure sensitive recording paper wherein chlorinateddiphenyl was used. Furthermore, even when this upper paper was exposedto sun light for a long time, the lowering in the color developingability and colored fog were not observed.

EXAMPLE 6 Example 1 was duplicated using2-methyl-5-isopropyldiphenylmethane (having a boiling point of 307 3 lOCand specific gravity of 09916 at 20C) instead of2,4-dimethyldiphenylmethane, and using 3-methyl- 2,2-spirobi(benzo[flchromene) instead of crystal violet lactone. The result thereof wasthe same as in Example 1.

EXAMPLE 7 Example 1 was duplicated, except that1,1-diphenyll-heptylmethane (having a boiling point of l43-l45C/0.lmml-lg, a melting point of to --4C and a specific gravity of 0.9444 at20C) was used instead of 2 ,4-dimethyldiphenylmethane. The resultthereof was the same as in Example 1.

wherein n is an integer of l to 8, R and R each represent a memberselected from the group consisting of alkyl groups containing one toeight carbon atoms, and a hydrogen atom, p and q represent the number ofalkyl groups, p q being an integer of 1 to 3, and R and R may be thesame.

2. The pressure sensitive recording paper as claimed in claim 1, whereinsaid compound is a member selected from the group consisting of:

CH3 CH:

C aHn C H; C Hz EXAMPLE 8 CH3 CH3 The result thereof was the same as inExample 1.

EXAMPLE 9 Example 1 was duplicated, except thatdimethyl-tbutyldiphenylmethane (mixture of several kinds of isomers,having a boiling point of l3 2l 48C/0.l mmHg) 3. The pressure sensitiverecording paper of claim 1, wherein said compound is used as a mixturewith a solvent selected from the group consisting of a petroleumfraction, a synthetic oil and a plant oil.

4. The pressure sensitive recording paper of claim 1, wherein said colorformer and said compound are contained in microcapsules.

5. The pressure sensitive recording paper of claim 3, wherein saidpetroleum fraction is a member selected from the group consisting ofliquid paraffin, kerosene and naphtha.

6. The pressure sensitive recording paper of claim 3, wherein saidsynthetic oil is a member selected from the group consisting ofchlorinated paraffin, chlorinated diphenyl, hexahydroterphenyl,alkylnaphthalenes and alkylated polyphenyls.

7. The pressure sensitive recording paper of claim 3, wherein said plantoil is a member selected from the group consisting of cottonseed oil andlinseed oil.

2. The pressure sensitive recording paper as claimed in claim 1, whereinsaid compound is a member selected from the group consisting of:
 3. Thepressure sensitive recording paper of claim 1, wherein said compound isused as a mixture with a solvent selected from the group consisting of apetroleum fraction, a synthetic oil and a plant oil.
 4. The pressuresensitive recording paper of claim 1, wherein said color former and saidcompound are contained in microcapsules.
 5. The pressure sensitiverecording paper of claim 3, wherein said petroleum fraction is a memberselected from the group consisting of liquid paraffin, kerosene andnaphtha.
 6. The pressure sensitive recording paper of claim 3, whereinsaid synthetic oil is a member selected from the group consisting ofchlorinated paraffin, chlorinated diphenyl, hexahydroterphenyl,alkylnaphthalenes and alkylated polyphenyls.
 7. The pressure sensitiverecording paper of claim 3, wherein said plant oil is a member selectedfrom the group consisting of cottonseed oil and linseed oIl.